DE69509227T2 - METHOD FOR PRODUCING A MULTI-LAYERED CIRCUIT BOARD FROM LAYERS REINFORCED WITH LATERAL FIBERS, LAYERS REINFORCED WITH LATERAL FIBERS AND AT LEAST ONE METAL MEDIUM LAYER - Google Patents

Abstract

The invention relates to a method of manufacturing a composite laminate having a plurality of UD layers, i.e., layers of matrix material reinforced with unidirectionally oriented fibres, and at least one inner metal layer, i.e., a metal layer that does not form an outer surface of the laminate, the layers being arranged so as to give a balanced and symmetric laminate. The method comprises passing through a laminating zone, preferably a double-belt press, unidirectionally oriented (UD) fibres provided with not yet consolidated matrix material and consolidating the matrix material. In a first step a non-flowing sandwich laminate of at least three layers is formed, the at least three layers being UD and metal layers, the sandwich laminate being formed by passing UD fibres provided with not yet consolidated matrix material through the laminating zone together with metal foil, and in a second step the non-flowing sandwich laminate is provided on its outer surfaces with UD layers, with additional UD layers optionally being added in subsequent steps.

Description

The invention relates to a method for producing a composite laminate with a plurality of UD layers, i.e. layers of matrix material reinforced with unidirectionally oriented fibers, and at least one inner metal layer, i.e. a metal layer that does not form an outer surface of the laminate, the layers being arranged to produce a balanced and symmetrical laminate, the method comprising guiding unidirectionally oriented (UD) fibers, not yet provided with solidified matrix material, through a lamination zone and solidifying the matrix material. The invention is aimed in particular at the production of printed circuit boards (PWBs) that have an inner metal layer. Such PWBs are known. The inner metal layer, usually a copper layer, serves as a ground plane, a power transmission plane or a heat sump and can have a hole pattern.

A method for producing a composite laminate in which unidirectionally oriented (UD) fibers are provided with matrix material that has not yet solidified and are guided through a laminating zone is known from EP 478 051. This document describes the continuous production of a flat substrate from a fiber-reinforced matrix, which method comprises the use of at least two moving layers of parallel, perpendicularly extending reinforcing fibers that are not bound in the form of a fabric (UD fibers), wherein the UD fibers, which are arranged in at least two intersecting directions, are provided with matrix material and then guided through a laminating zone, e.g. a double belt press, to form a cross-layer laminate. According to this method Laminates can be obtained that are excellently suited as PWB substrates, among other things because of their good surface properties, their comparatively low linear thermal expansion coefficient (TCE) in the x and y directions, the possibility of incorporating a high fiber content and their advantageous dimensional stability. The possibility that the laminate can contain an inner metal layer is briefly mentioned there, without a method for incorporating such an inner metal layer being described.

The type of PWB laminate described in EP 478 051 is known as a UD cross-ply PWB laminate. Such laminates contain matrix material reinforced with unidirectionally oriented filaments such that the UD reinforcing filaments are present in various layers of crossing orientation directions, the layers being symmetrically arranged with respect to a plane of symmetry through the center of the laminate extending parallel to the outer surfaces. Methods for making these UD cross-ply laminates are also described in various other publications.

Another method for producing a composite material reinforced with UD layers, which is also intended for use as a PWB substrate, is known from US 4,943,334. In this method, reinforcing filaments are wound around a rectangular flat core in several layers crossing each other at an angle of 90º, the filaments being provided with a curable matrix material by means of injection molding and/or impregnation. The matrix, which therefore has crosswise UD fibre layers, is then hardened.

Composite materials for PWBs in which individual, cross-arranged UD layers are used are known from US 4,814,945. This document relates to a resin reinforced with parallel fibers made of aramid used as a PWB substrate. Various resin layers are heated to the semi-cured or B-stage, and the UD-reinforced layers are placed on top of each other and then cured.

WO 92/22191 describes a method for producing a PWB laminate, which comprises preparing non-flowing UD layers, coating at least a portion of the non-flowing UD layers with an adhesive on one or both sides, cross-stacking the UD layers in such a way that at least one layer of adhesive is present between each pair of UD layers with different orientation directions, and bonding the stacked UD laminates by activating the adhesive layers.

The unpublished patent application PCT/EP93/01919 (publication number WO 94/02306) relates to a process for producing a composite laminate, preferably a cross-layer laminate, in which process unidirectionally oriented (UD) fibers are provided with matrix material and, together with a preformed, non-flowing UD composite or cross-layer laminate, are passed through a laminating zone into layers of at least two different orientation directions. Co-lamination with metal foil is mentioned as a possibility of using the laminates as PWB substrates, ie to make the outer surface of the formed laminate conductive.

EP 157 261 describes a laminating system for circuit boards, in which base plates and a length of foil are continuously fed so that the foil is laminated onto the surface of the base plate.

EP 158 027 describes a process for producing a copper-coated base material for printed circuit boards. A layer of resin reinforced with a woven glass fiber fabric is laminated with copper foil in a double belt press.

EP 52 738 describes a PWB laminate, in particular a multilayer PWB, with at least one inner conductive layer used as a power supply plane. The laminate is manufactured by stacking conventional insulating layers, such as prepregs, and pressing them with a copper plate having a thickness of 0.2 to 0.5 mm.

EP 264 105 describes a method for manufacturing a multilayer PWB containing a metal plate as an inner layer. The teaching of this patent is directed to the use of a metal plate having peripheral parts that extend beyond the final size of the PWB. The PWB is manufactured by stacking copper cores and prepreg layers.

EP 324 352 also describes a method for manufacturing a PWB with an inner layer of metal that serves as a heat conductor. The PWB is manufactured using conventional thermal molding processes.

Multilayer printed circuit boards comprising UD layers and conductive circuit layers are described in JP 01/283996, EP 374 319 and WO 92/22192.

The background art further includes processes for manufacturing laminates comprising layers of reinforced plastics and metal layers.

Thus, EP 447 642 describes the formation of a "sandwich structure" consisting either of a metal layer enclosed between two layers of a reinforced thermoplastic material or of a reinforced thermoplastic layer enclosed between two metal layers. The reinforcements are fabrics and the like, UD layers are not described. The process involves the joining of different layers and pressing them together at a temperature above the melting point of the thermoplastic resin.

US 4,402,778 describes a method for producing laminated structures containing reinforcing plastic sheets. The method involves placing a plate, which may be a metallic sheet, in a double belt press together with two fiber-reinforced plastic sheets enclosing the plate. The sheets may contain any type of reinforcing material.

US 5,024,714 describes a method for forming a composite component, the method comprising continuously feeding metal sheets and continuously extruding plastic sheets, whereby these metal sheets and plastic sheets are alternatively laminated. The plastic sheets may contain reinforcement which may be in the form of parallel fibers.

EP 347 936 describes the continuous manufacture of a laminated sheet, in which process several resin-impregnated fibrous base layers are laminated in a double belt press, optionally with a metal foil which represents the outermost layer of the laminated sheet.

A laminate containing UD layers is described in FR 1,691,813. The UD layers are supported by a film, which can be paper, plastic or metal, for example.

None of the above-mentioned prior art documents describes a method for producing PWBs that have at least one inner metal layer based on laminates that have UD reinforcement.

The invention aims to provide such a method. In particular, the aim of the invention is to provide a method that allows the orientation of the fibers (filaments) in the UD layers to be maintained. The method should enable the production of balanced and symmetrical laminates in a simple manner and be sufficiently adaptable to accommodate different configurations of UD layers and metal layers. Another goal is to offer a process that allows (semi-)continuous production.

With this aim, the method according to the invention is characterized in that in a first step a non-flowing sandwich laminate is formed from at least three layers, the at least three layers being UD and metal layers, the sandwich laminate being formed by passing UD fibers, which are provided with matrix material that has not yet solidified, together with the metal foil through the lamination zone and in a second step the non-flowing sandwich laminate is provided with UD layers on its outer surfaces, further UD layers being able to be added in subsequent steps if desired. This "lay-on" UD method is described in more detail below.

To facilitate this explanation, the following abbreviations are used:

M metal;

FR UD fibers containing resin that has not yet solidified;

UD non-flowing UD layer;

x Manufacturing direction (also called "0º" orientation );

x perpendicular to the production direction (also called "90º" orientation),

The term "side" when used in connection with the lamination zone does not refer to the inlet and outlet sides of the zone, but to the sides of the resulting laminate to be laminated. For example, if the platen press is arranged horizontally, the two "sides" are the lower and upper plates. If the laminating zone is a double belt press, the "sides" refer to the two belts.

The method of the invention meets the requirement that the orientation of all UD layers can be maintained: the UD fibers, which are provided with matrix material that has not yet solidified, are placed under tension as a result of being passed through the lamination zone and, as a result, the orientation is fixed by the matrix resin no longer being flowable. In order to make maximum use of this advantage of the method according to the invention, it is preferred to carry out the lamination in a double belt press and to unwind the UD fibers in the form of continuous filaments from a spool. Compared to the prior art, the method according to the invention thus offers a simpler and superior maintenance of the orientation that is so important for the production of composite materials reinforced with UD fibers.

In the first step, a UD-metal-UD laminate can be produced as follows: UD fiber-containing but not yet solidified matrix material is arranged symmetrically with respect to the outer surfaces of a metal foil. The resulting stack of layers (FRx-M-FRx) is passed through the lamination zone and the matrix resin is solidified so that a UDx-M-UDx sandwich laminate is formed in a non-flowable state. In a subsequent step, UD layers are added, i.e. the UD-M-UD sandwich laminate is fed through the lamination zone while FR layers are fed on both sides of the sandwich laminate. In order to achieve the desired balance (the same proportion of resin and fibres in 0º and 90º directions) and symmetry (with respect to a plane of symmetry through the centre of the laminate extending parallel to its outer surfaces), a measured part of the sandwich laminate (manufactured as a UDx-M-UDx laminate) can be formed (e.g. by cutting to a length equal to the width) and introduced into the lamination zone after rotation through 90º, i.e. as a UDy-M-UDy sandwich laminate.

From a practical point of view, it is preferred that the orientation direction of the fibers to be provided with matrix material is the same as the machine direction during the lamination process. Thus, a stack containing FRx-UDy-M-UDy-FRx is passed through the lamination zone to form a UDx-UDy-M-UDy-UDx laminate. When a thicker laminate is produced, i.e. when several UD layers are added in subsequent stages, it does not matter at which stage the orientation direction is changed, as long as the required balance and symmetry are achieved.

Alternatively, the first step may result in the formation of a metal-UD-metal sandwich laminate. One possibility is that a metal foil is fed together with an FR layer and added on one side, while a bare metal foil is added on the other side. However, since the process of the invention preferably works in symmetrical tric manner (simultaneously adding the same material to both sides at each stage), it is preferred that the stack of plies fed through the lamination zone is of the M-FRx-FRx-M type. After solidification to the non-flowing state, this results in an M-UDx-UDx-M sandwich laminate (i.e. an M-UD-M sandwich in which the central UD ply has a double thickness). To form a balanced and symmetrical laminate, the M-UDx-UDx-M laminate can be cut into rectangular pieces which - rotated by 90º, i.e. as an M-UDy-UDy-M sandwich laminate - are fed back through the lamination zone together with FR plies. This FRx-M-UDy-UDy-M-FRx stack results in the formation of a balanced and symmetrical laminate having two inner metal layers: UDx-M-UDy- UDy-M-UDx.

The term "non-flowing" is used to mean that the matrix material is solidified (consolidated) to such an extent that it cannot be made to flow again during the remainder of the manufacturing process. In general, this means that the non-flowing material is present during storage and processing under such pressure and temperature conditions that the matrix resin is in a state below its softening point (i.e. below the Tg or apparent Tg). The various stages of the matrix material (matrix resin) are commonly referred to in the art as "A", "B" and "C" stages, with the A stage denoting the unsolidified resin (i.e. in the case of a thermosetting resin: the uncured state), the B stage generally indicates partial solidification (in the case of a thermosetting resin: the reaction has led to the formation of longer chains but not yet to complete cross-linking), and the C stage means a solidified (hardened) state. For convenient storage and processing, it is preferred for the solidification of the non-flowing material that the resin has reached the C stage, or that resins with rigid molecular chains are used which, under normal storage and processing conditions, already reach a non-flowing state in a stage that is still referred to as the B stage. However, if the pressing in the lamination zone is carried out under isobaric conditions, material in the A stage can also be used. The terms A stage, B stage and C stage are known in the art and require no further explanation here.

The term "not yet solidified matrix material" refers to a matrix material with a viscosity that is sufficiently low under the conditions of application to the UD fibers to enable impregnation, such that thermoplastic resins are in a liquid state. Not yet solidified thermosetting resins are generally in the A or B stage (with the exception of the thermosetting resins mentioned above, which are no longer flowable even in the B stage).

It should be noted that the guiding of UD fibres, which are provided with a matrix material that has not yet solidified, through the lamination zone allows the production of a non-flowing material rial that is not subject to restrictive requirements with regard to adhesiveness, while allowing sufficient adhesion of unsolidified matrix material. The unsolidified matrix material is generally liquid, but could also be in the form of a free-flowing powder that can be applied to UD fibers.

In general, it is advisable to post-cure the composite laminate produced by the process according to the invention after the final lamination step in order to ensure complete conversion in all layers.

An additional advantage of the processing according to the invention is that the process is suitable for the use of high molecular weight resins without solvents as well as for catalysed resins (of importance in the case of electroless additive metallisation). Such commercially important resins give insufficient impregnation in processes in which different UD layers are stacked on top of each other and subsequently impregnated (as described in the above-mentioned EP 478 051).

It is irrelevant how the fibers provided with the matrix material, which are passed through the lamination zone together with the preformed, non-flowing material, are obtained. One possible method is to coat a fiber bed with matrix material, another method is to pass individual fibers through a bath containing matrix material. Alternatively, a UD prepreg can also be used here. It is It is preferred that the fibers are passed through a feed zone during or after they are provided with the matrix material. The feed zone may include means for filament distribution and for adjusting tension and orientation. Preferably, a non-pressurized, preheated feed zone is used. A suitable heating means is heating with a direct gas flame.

Preferably, the PWB laminate is prepared such that the UD reinforced layers are oriented as specified in one of the following models, where 0º and 90º represent perpendicular orientation directions and the relative thickness of the layers is indicated, where necessary, by repeating the given orientation:

0º/90ºCu90º/0º (or UDx-UDy-M-UDy-UDx);

0º/90º90º/0ºCu0º/90º90º/0º (or UDx-UDy-UDy-UDx-M-UDx-UDy-UDy-UDx);

0º/Cu90º90ºCu/0º (or UDx-M-UDy-UDy-M-UDx);

0º/90º/0º/Cu90º90ºCu/0º/90º/0º (or UDx-UDy-UDx-M-UDy-UDy- M-UDx-UDy-UDx).

In general, the UD reinforced layers for use in the PWBs in laminates according to the invention each have a thickness in the range of 6 to 800 µm, preferably about 15 to 400 µm.

The inner metal layers may generally have a thickness in the range of about 12 µm to 1 mm. For heat dissipation layers, the larger thicknesses are preferred. A thickness of about 1 mm is preferred when the metal layer is aluminum foil and is used for heat dissipation. When the When the first layer is a copper layer, thicknesses of the order of 70 µm, 140 µm, 210 µm and lower thicknesses, e.g. about 18 µm, for grounding or connection planes are preferred for heat distribution. In the case of copper foil, it is highly preferred that double-treated copper foil is used to enable good adhesion of the matrix resin on both sides without the use of adhesives or adhesion promoters.

Particularly advantageous results can be obtained if, in the process according to the invention, a double belt press is used as the laminating zone for all the process steps described above.

It should be noted that double belt presses are known to those skilled in the art and no further general explanation is required here. The method of the invention can also be carried out with other types of laminating zones, but the use of a double belt laminating zone (not necessarily with a pressure effect) is preferred.

Alternatively, the product manufactured by the process according to the invention (UD metal-UD sandwich laminate, UD metal-UD metal-UD sandwich laminate or the ultimately resulting cross-ply laminate) can be subjected to a surface treatment to improve the adhesion. Such treatments, e.g. corona treatment and low-pressure plasma treatment, are known. They are most conveniently applied downstream of the lamination zone and before the application of any coatings.

It may be advantageous to pretreat the tapes in the lamination zone with a release agent. Release agents are well known and come in two main forms, namely those which are transferred to the material passing through the lamination zone and those which are not. The latter are preferred although the former may also be used to advantage if a surface treatment as described above is to follow and any transferred release agent can be removed during such treatment. Alternatively, a release film may be carried to prevent adhesion to the tapes in the lamination zone.

The materials used in the practice of the present invention are not particularly critical. Preferably, the materials described below are used.

The matrix material is a thermoplastic or a thermosetting polymer, with thermosetting resins being preferred. Even more preferred is the use of a matrix material based on epoxy resin, but in principle other resins are also usable. Examples include cyanate esters, unsaturated polyester (UP) resins, vinyl ester resins, acrylate resins, BT epoxy resins, bismaleimide resin (BMI), polyimide (PI), phenolic resins, triazines, polyurethanes, silicone resins, biscitracone resin (BCI). Alternatively, combinations of the resins mentioned can be used, and it is also possible to mix the above resins with certain suitable thermoplastics, such as PPO, PES, PSU and PEI, among others. It is also advantageous to incorporate compounds into the matrix material. compounds which make it flame resistant, such as phosphorus or halogen (especially bromine) containing compounds. A special matrix material, which is preferred because of its favorable flow and curing properties, contains about 100 parts by weight of Epikote®828 EL, about 73 parts by weight of Epikote®5050 and about 30 parts by weight of isophoronediamine.

With regard to the addition of flame retardant compounds, in particular bromine compounds, it is further noted that such compounds should only be used in minimal proportions in view of their adverse effects on the environment. The method according to the invention is advantageous in this respect in that it enables different layers in the laminate to be joined together in such a way that only the outer layers are substantially flame resistant, which is sufficient to prevent the laminate from catching fire. Such a step can also be carried out in the case of multilayer PWBs.

Fillers can be added to the matrix material in the usual way, e.g. quartz powder and glass powder, such as borosilicate glass powder. Furthermore, the matrix can be made catalytic for the electroless copper coating, e.g. by adding precious metal or precious metal compounds, in particular palladium or its compounds.

Although the preferred reinforcing materials consist of filament yarns (untwisted strands), non-continuous fibers may also be used. According to the invention, the reinforcing yarns may preferably consist of the The following material groups can be selected: glass, e.g. E-glass, A-glass, C-glass, D-glass, AR-glass, R-glass, S1-glass and S2-glass, as well as various ceramic materials such as aluminum oxide and silicon carbide. Also suitable for use are polymer-based fibers, in particular the so-called liquid crystalline polymers such as paraphenylene terephthalamide (PPDT), polybenzobisoxazole (PBO), polybenzobisthiazole (PBT) and polybenzoimidazole (PBI), as well as fibers based on polyethylene naphthalate (PEN), polyethylene terephthalate (PETP) and polyphenylene sulfide (PPS).

Generally, the fiber content in the matrix is about 10-90 vol.% and is preferably in the range of about 40 to about 70 vol.%. A fiber volume fraction of about 50 vol.% is highly satisfactory.

The invention also relates to multilayer PWBs (MLBs). In particular, composite laminates according to the invention are very suitable for use in the method specified in WO 92/22192, which document is incorporated herein by reference. According to this method, a hard-base substrate provided with conductive paths on both sides is laminated with an intermediate substrate such that the intermediate substrate has a hard core layer with a still plastically deformable adhesive layer at least on the side facing the conductive paths on the base substrate, and pressure is applied to the laminate such that the hard core layer of the intermediate substrate comes into contact or virtually into contact with the conductive paths of the base substrate and the voids between the conductive paths are filled with the adhesive material. which joins the base substrate and the intermediate substrate together. The cross-ply laminates according to the invention which contain metal layers are highly suitable for use in the base substrate as well as in the intermediate substrates. Accordingly, the invention also relates to the use of a UD cross-ply laminate produced by the method as described above for producing an adhesive-insulated panel.

The flowable adhesive layer which fills the gaps can of course also be applied to the existing laminates if desired. However, the process described above, in which an adhesive layer can advantageously be applied to a composite laminate, is highly suitable for use in the manufacture of the intermediate substrates which are provided with the adhesive or adhesive filling the gaps. Preferably, the base substrate provided with paths is a PWB which is also manufactured according to the process according to the invention. Numerous polymers are suitable for use as the adhesive filling the gaps, in particular thermosets such as epoxy resin (EP), polyurethane (PU), vinyl ester (VE), polyimide (PI), bismaleimide (BMI), biscitraconimide (BCI), cyanate esters, triazines, acrylates and mixtures thereof. A wide variety of additives can be added before the adhesive is applied, e.g. catalysts, inhibitors, surfactants, thixotropic agents and in particular fillers. The fillers are preferably selected from the following material group: quartz powder, glass powder, ceramic powder, such as aluminum minium oxide powder. The fillers to be used should preferably have a low coefficient of thermal expansion and a low dielectric constant. Favorable results can be achieved by using hollow spheres as fillers, whereby the spheres can consist either of a polymer or a ceramic material or of glass. Expandable polymer powders are particularly suitable for use as fillers.

Furthermore, the composite laminates produced using the method according to the invention are eminently suitable for use as carrier material in devices having various integrated circuits thereon (multichip modules). This is due in particular to the favorable thermal expansion coefficients, which are predominantly the result of the high fiber volume fraction that can be achieved by using cross-layer laminates, and which are approximately equal to the thermal expansion coefficients of electronic components (chips) used together with PWBs, in particular MLBs. Such components can be arranged on top of an MLB (chip-on-board) or otherwise embedded in a substrate, such as an intermediate substrate according to WO 92/01133 (chip-in-board). Furthermore, the method according to the invention and the composite laminates obtained by its application can be used for so-called mass lamination (masslam). In this process, a layer provided with electrically conductive paths on both sides is generally laminated with prepreg on the sides provided with these paths. According to the invention, the masslam process can advantageously be carried out in a continuous or non-continuous manner. continuous operation, in which a layer provided with electrically conductive paths on both sides is passed through the lamination zone instead of or in combination with the preformed non-flowing composite and is provided on each side with a layer of matrix material containing UD fibers, especially when using a double belt press. In a subsequent lamination step, the PWBs thus produced and provided with UD layers can be laminated again with UD layers, this time with the opposite orientation, essentially as described above.

The invention is further explained with reference to the drawings. The drawings are for illustrative purposes only and are not to be considered restrictive in any way.

Fig. 1 relates to a preferred embodiment of the invention in which a single double belt press is used both for the production of a UD-metal-UD sandwich laminate and for the resulting UD cross-layer laminate containing a metal layer and symmetrical in the midplane.

The figure shows a cross-section parallel to the machine direction of an apparatus with which the method according to the invention can be carried out. A description of the illustrated embodiment of the method is given below together with the component parts of the apparatus.

Formation of the UD-metal-UD sandwich laminate:

The packages (2) are unwound from two reels (1), preferably in a rolling manner, and thus form a unidirectional bed of filament bundles (3), which is converted into a homogeneous unidirectional filament bed (5) with the aid of a yarn distributor (4). A matrix film (7) is presented on an endless belt (8) or on a film strip (9) by means of a coating unit (6), which is unwound from twin delivery holders (10), after which the matrix film (7) is brought together with the homogeneous unidirectional filament bed (5).

Impregnation and deaeration take place in the heated zone (11). The two matrix-impregnated UD filament layers (12) are brought together with copper foil (20a) and then passed through the heated lamination zone (13). The copper foil (20a) is passed through the lamination zone (13) in such a way that it is provided with impregnated UD fibers (12) on both sides. In the lamination zone (13), the two UD layers and the copper foil are fused together to form a UD-metal-UD sandwich laminate.

The product is then guided through the cooling zone (14), which it leaves as a practically continuous belt (15). This belt is cut (16) and stored (17) (e.g. in a box or on a pallet).

Formation of the cross-ply laminate:

The procedure is the same as described above, up to the introduction of the impregnated UD fibers into the lamination zone (13). Instead of copper foil (20a), a box (19) passes plates of non-flowing UD metal-UD sandwich laminate, rotated by 90º relative to the machine direction (20b), through the laminating zone (13) so that the plates are provided with impregnated UD fibers (12) on both sides, whereby the orientation direction of the UD fibers in the plates (18) is consequently perpendicular to the orientation of the impregnated UD fibers (12). The pressed material is then treated as described above to form the finally obtained cross-layer laminate (not shown separately in the figure). This procedure can be repeated until the desired number of layers or the desired product thickness is achieved.

Depending on the end use of the laminate, it can be provided with an adhesive layer using a double-side coater (21), if desired in a dust-free room (22). Such an adhesive layer can be the "additive adhesive" described above for electroless copper plating, but can also be an adhesive as described in WO 92/22192 for the production of multilayer PWBs. Alternatively, a photosensitive layer (photoresist) can be applied in this way.

Fig. 2 shows in cross section various base materials that can be produced and used according to the method according to the invention.

Fig. 2a shows a UD-metal-UD sandwich laminate comprising a 0º UD layer (201), a metal layer (202) and a 0º UD layer (203).

Fig. 2b shows a metal-UD-metal sandwich laminate containing a metal layer (204) and a 0º UD layer (205) and as a result of the applied process has a double thickness and contains a metal layer (206).

Fig. 2c shows a UD-metal-UD-metal-UD sandwich laminate made by adding UD layers to the laminate of Fig. 2b and containing a 90º UD layer (207), a metal layer (204), a 0º UD layer (205), a metal layer (206) and again a 90º UD layer (208).

Fig. 2d shows an alternative to Fig. 2c, according to which the outer UD layers (209 and 210) have a 0º direction.

Fig. 3 shows the resulting cross-ply laminates.

Fig. 3a shows a laminate with an outer metal layer (211), a 0º UD layer (212), a 90º UD layer (213), an inner metal layer (214), a 90º UD layer (215), a 0º UD layer (216) and an outer metal layer (217).

Fig. 3b shows a laminate with an outer metal layer (218), a 90º UD layer (219), a 0º UD layer (220), a 90º UD layer (221), a metal layer (222), a double thickness 0º UD layer (223), a metal layer (224), a 90º UD layer (225), a 0º UD layer (226), a 90º UD layer (227) and an outer metal layer (228).

Fig. 3c shows a laminate with an outer metal layer (229), a 90º UD layer of double thickness (230), a 0º layer (231), a metal layer (232), a 0º UD layer of double thickness (233), a metal layer (234), a 0º UD layer (235), again a 90º layer of double thickness (236) and an outer metal layer (237).

Claims (19)

1. Process for producing a composite laminate with a plurality of UD layers, i.e. layers of matrix material reinforced with unidirectionally oriented fibers, and at least one inner metal layer, i.e. a metal layer which does not form an outer surface of the laminate, wherein the layers are arranged so that they result in a balanced and symmetrical laminate, in which process unidirectionally oriented (UD) fibers (5) provided with not yet solidified matrix material (7) are guided through a laminating zone and the matrix material is solidified, characterized in that in a first step a non-flowing sandwich laminate is formed from at least three layers, where the at least three layers are UD (201, 203, 205) and metal layers (202, 204, 206) and all fibers in the non-flowing sandwich laminate have a single orientation direction, wherein the sandwich laminate is formed by guiding UD fibers provided with not yet solidified matrix material together with metal foil (9) through the lamination zone (13), and wherein in a second step the non-flowing sandwich laminate is provided with UD layers (207/208, 209/210) on its outer surfaces, wherein if desired, additional IM layers are added in subsequent steps. 2. Method according to claim 1, characterized in that the lamination process is carried out using a double belt press. 3. Method according to claim 2, characterized in that in the lamination zone along the two outer surfaces of the non-flowing sandwich laminate, not yet solidified matrix material is introduced, which is provided with UD fibers that have an orientation direction that runs approximately perpendicular to the orientation direction in the sandwich laminate. 4. Method according to one of claims 1 to 3, characterized in that a UD-metal-UD sandwich laminate is formed by guiding a metal foil between two layers of UD fibers which are provided with unconsolidated matrix material and guiding the metal foil, which is thus UD-reinforced on both surfaces and contains unconsolidated matrix material, through the lamination zone. 5. Method according to claim 4, characterized in that in the lamination zone along the two outer surfaces of the non-flowing UD-metal-UD sandwich laminate (201, 202, 203) non-solidified matrix material is introduced, which is provided with UD fibers that have an orientation direction that runs approximately perpendicular to the orientation direction of the UD-metal-UD sandwich laminate. 6. Method according to claim 5, characterized in that the measured part of the UD-metal-UD sandwich laminate is formed by cutting an endless UD-metal-UD sandwich laminate which in the first step is a length approximately equal to the width. 7. Method according to one of claims 1 to 3, characterized in that in the first step a metal-UD-metal sandwich laminate is formed, the metal-UD-metal sandwich laminate containing a UD layer (205) sandwiched between two conductive metal layers (204, 206) by passing two sheets or strips of metal foil through the lamination zone, passing the UD fibers provided with not yet solidified matrix material which are between them. 8. Method according to claim 7, characterized in that in the second step, a UD-metal-UD-metal-UD laminate is formed, the UD-metal-UD-metal-UD laminate, which contains the metal-UD-metal sandwich laminate (204, 205, 206), is arranged in a sandwich-like manner between two UD layers (207/208, 209/210) by guiding UD fibers, which are provided with not yet solidified matrix material, together with the metal-UD-metal sandwich laminate through the lamination zone. 9. Method according to one of claims 2-8, characterized in that the double belt press has an isobaric lamination zone. 10. Method according to claim 9, characterized in that a viscous thermoplastic polymer is carried along the edges of the material guided through the double belt press parallel to the machine direction. 11. Method according to one of claims 1-10, characterized in that the metal foil is a double-treated copper foil. 12. Method according to one of claims 2-11, characterized in that the composite laminate is made suitable for the production of multilayer PWBs by providing its outer sides downstream of the lamination zone (21, 22) with an adhesive layer which still has to be made to flow. 13. A method for producing a printed circuit board, characterized in that a composite laminate according to one of claims 1-12 is produced, in which at least one outer surface of the composite laminate has been made suitable for applying paths made of electrically conductive material. 14. A method according to claim 13, characterized in that a foil made of a metal suitable for the subtractive formation of conductive paths is laminated on the outer sides of the fibrous matrix material which is guided through the lamination zone. 15. Method according to claim 13, characterized in that the composite laminate is provided with a base layer on the outside after passing through the lamination zone in order to promote the adhesion of electrolessly deposited copper paths. 16. Multilayer PWB comprising at least three layers of patterned conductive material and at least two spacer layers containing insulating material, characterized in that at least one spacer layer also has a conductive metal foil layer, the spacer layer being manufactured using the method according to one of claims 1-3. 17. Use of a composite laminate produced by a process according to any one of claims 2-11, for producing a printed circuit board. 18. Use of a composite laminate produced by a process according to any one of claims 2-11, for producing an adhesive-coated spacer plate for a multilayer PWB. 19. A substrate for a printed circuit board (a PWB) comprising a composite laminate, at least one outer surface of which has been made suitable for the deposition of paths of conductive material, the composite laminate comprising matrix material so reinforced with unidirectionally oriented fibers, and the UD reinforcing filaments being present in different layers with mutually crossing orientation directions, the layers being symmetrically arranged with respect to a plane of symmetry through the center of the laminate which extends parallel to their outer surfaces, characterized in that the laminate has, in addition to the layers of UD filaments, two inner metal layers, the metal layers being arranged relative to the The plane of symmetry is arranged symmetrically and in a mirror image.